ZEOLITE SYNTHESIS IN A REACTOR WITH CONTROLLED VELOCITY PROFILE

Abstract

The present invention relates to a process for the preparation of a zeolitic material, as well as to a catalyst per se as obtainable or obtained according to said process. Furthermore, the present invention relates to the use of the zeolitic material, in particular as a catalyst.

Claims

1: A process for preparing a zeolitic material having a framework structure comprising YO.sub.2 and optionally comprising X.sub.2O.sub.3, wherein Y is a tetravalent element and X is a trivalent element, said process comprising: (i) preparing a mixture comprising a source of YO.sub.2, optionally a source of X.sub.2O.sub.3, and a liquid solvent system; (ii) feeding the mixture prepared in (i) as a reaction mixture into a reactor; (iii) heating the reaction mixture in the reactor, to obtain a reacted mixture comprising a zeolitic material having a framework structure comprising YO.sub.2 and optionally comprising X.sub.2O.sub.3; and (iv) collecting the reacted mixture obtained in (iii) as an effluent from the reactor; wherein the reactor is a Taylor-Couette reactor comprising an inner cylinder and an outer cylinder which are coaxially aligned.

2: The process of claim 1, wherein the Taylor-Couette reactor has a rotor-stator set-up, with the outer cylinder as a stator.

3: A process for preparing a zeolitic material having a framework structure comprising YO.sub.2 and optionally comprising X.sub.2O.sub.3, wherein Y is a tetravalent element and X is a trivalent element, said process comprising: (i) preparing a mixture comprising a source of YO.sub.2, optionally a source of X.sub.2O.sub.3, and a liquid solvent system; (ii) feeding the mixture prepared in (i) as a reaction mixture into a reactor; (iii) heating the reaction mixture in the reactor, to obtain a reacted mixture comprising a zeolitic material having a framework structure comprising YO.sub.2 and optionally comprising X.sub.2O.sub.3; and (iv) collecting the reacted mixture obtained in (iii) as an effluent from the reactor; wherein, in (iii): the reaction mixture is subjected to shearing so as to create a flow of the reaction mixture relative to an outer wall of the reactor with which the reaction mixture is in contact; when the reaction mixture displays a shear thinning rheology (pseudoplastic rheology), a velocity profile v(r) of the reaction mixture in a direction of flow satisfies the following condition (I):
v(r)((v(r.sub.1)v.sub.min).Math.(r/r.sub.1))+v.sub.min(I); and when the reaction mixture displays a shear thickening rheology (dilatant rheology), the velocity profile v(r) of the reaction mixture in the direction of flow satisfies the following condition (II):
v(r)((v(r.sub.1)v.sub.min).Math.(r/r.sub.1))+v.sub.min(ii), wherein r defines a length of a straight line in a cross-sectional area of a reactor space perpendicular to the direction of flow, wherein said straight line extends from a first point at an inner surface of the outer wall, wherein at said first point r.sub.0 is defined as 0 and v exhibits its minimum value (v.sub.min=v(r.sub.0)), to a second point where r is defined as r.sub.max and v exhibits its maximum value (v.sub.max=v(r.sub.max)), wherein r.sub.1=r.sub.max/x, and x=5.

4: The process of claim 3, wherein the straight line r is perpendicular to the inner surface of the outer wall.

5: The process of claim 3, wherein, in (iii): when the reaction mixture displays a shear thinning rheology (pseudoplastic rheology), a second derivative v(r) of the velocity profile satisfies the following condition (III):
v(r)0(III); and when the reaction mixture displays a shear thickening rheology (dilatant rheology), the second derivative v(r) of the velocity profile satisfies the following condition (IV):
v(r)0(IV).

6: The process of claim 3, wherein the reactor is a Taylor-Couette reactor comprising an inner cylinder and an outer cylinder which are coaxially aligned.

7: The process of claim 1, wherein, in, a flow regime in at least a portion P of a volume of the reactor is laminar.

8: The process of claim 1, wherein, in, a Reynolds number (Re) in at least a portion P of a volume of the reactor is 2,500 or less.

9: The process of claim 8, wherein, in (iii), a Taylor number (Ta) in at least the portion P satisfies the following condition (III):
Ta(1.52.Math.Re)+n(III) wherein n102.

10: The process of claim 1, wherein the mixture is heated to a temperature in a range of from 100 to 300 C.

11: The process of claim 1, wherein a volume of the reactor is in a range of from 5 cm.sup.3 to 1 m.sup.3.

12: The process of claim 1, wherein, in (iii), the reaction mixture is heated under autogenous pressure.

13: The process of claim 1, wherein the process is conducted in a continuous mode and/or in a batch mode.

14: A zeolitic material, obtainable and/or obtained by the process of claim 1.

15: A method of producing a molecular sieve, an adsorbent, a catalyst and/or a catalyst support, the method comprising obtaining the zeolitic material of claim 14.

Description

DESCRIPTION OF THE FIGURES

[0189] FIG. 1 displays the general set-up of the Taylor-Couette reactor wherein the inlet for the reaction mixture is depicted at the upper right portion of the reactor and the outlet is depicted at the lower left portion of the reactor. In the figure, the arrows describe the incremental direction of flow of the reaction mixture in the gap between the inner rotor of the reactor depicted as a hollow tube, and the outer mantel (stator) depicted as a transparent shell for displaying the reactor volume between rotor and stator. The scale at the bottom of the figure displays the dimensions of the reactor used for the simulation in meters.

[0190] FIG. 2 displays the rheology of the reaction mixture used in for the simulation in the experimental section, wherein the viscosity in Pa.Math.s is plotted along the abscissa, and the shear rate in s.sup.1 is plotted along the ordinate. In the figure, the function of the viscosity behavior in dependence on the shear rate is shown.

[0191] FIG. 3 displays the velocity contour of the reaction mixture in the Taylor-Couette reactor for the simulation of Example 1, wherein the scale in the figure indicates the velocity in m.Math.s.sup.1, which ranges from 0 to 0.6177 m.Math.s.sup.1. The scale at the bottom of the figure displays the dimensions of the reactor used for the simulation in meters.

[0192] FIGS. 4, 6, and 8 display the temperature contour of the reaction mixture in the Taylor-Couette reactor for the simulation of Examples 1, 2, and 3, respectively, wherein the scale in the figure indicates the temperature in degrees kelvin (K), which ranges from 300 to 500 K. The scale at the bottom of the figure displays the dimensions of the reactor used for the simulation in meters.

[0193] FIG. 5 displays the velocity contour of the reaction mixture in the Taylor-Couette reactor for the simulation of Example 2, wherein the scale in the figure indicates the velocity in m.Math.s.sup.1, which ranges from 0 to 0.7616 m.Math.s.sup.1. The scale at the bottom of the figure displays the dimensions of the reactor used for the simulation in meters.

[0194] FIG. 7 displays the velocity contour of the reaction mixture in the Taylor-Couette reactor for the simulation of Example 3, wherein the scale in the figure indicates the velocity in m.Math.s.sup.1, which ranges from 0 to 0.82965 m.Math.s.sup.1. The scale at the bottom of the figure displays the dimensions of the reactor used for the simulation in meters.

[0195] FIG. 9 displays the results of the viscosity measurements obtained in Reference Example 1 for different shear rates. In the figure, temperature measurement points are displayed with .square-solid. and the viscosity measurement points with .circle-solid., wherein the temperature values in C. are plotted along the right abscissa, and the viscosity values in Pa.Math.s are plotted along the left abscissa. The duration of the viscosity measurement in minutes is plotted along the ordinate. In the legend, the different viscosity measurement points for shear rates of 250, 500, and 750 s.sup.1 are indicated, wherein the measurement for the shear rate of 250 s.sup.1 was interrupted after 119 minutes, and the measurement for the shear rate of 750 s.sup.1 was interrupted after 142 minutes. The dotted line in the figure indicates the viscosity level of the reaction mixture at the beginning of the measurement prior to heating.

EXPERIMENTAL SECTION

[0196] The experiments described herein were conducted with the simulation program Ansys Fluent v17.0.0. The simulations were based on a Taylor-Couette reactor set-up as shown in FIG. 1 with an inner rotor and outer stator, wherein the reaction mixture was introduced at one end of the reactor (upper right of the reactor in FIG. 1) and was allowed to flow concentrically around the rotor within the reactor volume, and to spiral down to the reactor oulet (lower left or the reactor in FIG. 1). The parameters used for the simulation are as follows:

[0197] Cylinder Geometry: [0198] Length=25 cm [0199] D.sub.inner=5 cm [0200] D.sub.outer=6 cm [0201] Volume=0.00027 m.sup.3, Area=0.09 m.sup.2

[0202] Target Reaction Time: [0203] Tau=5 min (300 s) [0204] Feed=0.6 g/s (36 ml/min)

[0205] Temperatures: [0206] Wall 500 K (227 C.) [0207] Feed 300 K (27 C.)

[0208] Pressure Drop: 1550 Pa

[0209] Material Properties (Non-Newtonian Behaviour): [0210] Consistency Index 1.1 [0211] Power-Law Index 0.252

[0212] The viscosity characteristics of the reaction mixture used in the simulations is displayed in FIG. 2.

Example 1: Simulation with Low Taylor Number

[0213] A simulation was conducted with the reaction set-up described above, wherein the shear rate of the Taylor-Couette reactor was set such that the Reynolds number (Re) of the reaction mixture was Re=2.3, and the Taylor number (Ta) of the reaction mixture was Ta=1. The velocity contour obtained according to the simulation is displayed in FIG. 3, and the temperature contour is shown in FIG. 4. Thus, as may be taken from the results of the simulation displayed in FIG. 3, under the conditions chosen the reaction mixture displays a substantially homogenous velocity profile along the entire length of the reactor volume, with values around 0.6 m.Math.s.sup.1, which indicative of a laminar flow regime of the reaction mixture substantially along the entire length of the reactor. As may be taken from the temperature contour displayed in FIG. 4, the reaction mixture displays a gradual increase in temperature from the upper inlet region displaying temperature values of around 350 K to the lower outlet region displaying values of around 460 K.

Example 2: Simulation with High Taylor Number

[0214] A further simulation was conducted with the reaction set-up described above, wherein the shear rate of the Taylor-Couette reactor was set such that the Reynolds number (Re) of the reaction mixture was Re=2.6, and the Taylor number (Ta) of the reaction mixture was Ta=111. The velocity contour obtained according to the simulation is displayed in FIG. 5, and the temperature contour is shown in FIG. 6. Thus, as may be taken from the results of the simulation displayed in FIG. 5, under the conditions chosen the reaction mixture displays an irregular velocity profile along the length of the reactor volume, wherein the velocity regularly oscillates between values of around 0.4 m.Math.s.sup.1 and values of around 0.7 m.Math.s.sup.1. As opposed to the results obtained in Example 1, said velocity contour is indicative of an at least intermittently if not substantially turbulent flow regime of the reaction mixture along the entire length of the reactor. Furthermore, as may be taken from the temperature contour displayed in FIG. 6, as opposed to the results obtained in Example 1, substantially no temperature gradient may be obtained under these simulation conditions, the temperature being around 500 K along the entire length of the reactor volume.

Example 3: Simulation of a Change of the Reaction Mixture from Aqueous Solution to Gel

[0215] An additional simulation was conducted, wherein the rheology of the reaction mixture was varied to simulate a transition from the rheology of an aqueous solution to the rheology of a gel as is typically encountered during the course of crystallization of zeolitic materials from an aqueous solution or slurry containing the precursor compounds. In particular, the rheology was simulated such that in the first third of the reactor volume from the inlet end displayed a rheology typical of an aqueous solution, and the last two thirds of the reactor volume down to the outlet of the reactor display a rheology typical of a gel. For this purpose, no heating of the reaction mixture was applied in the first third of the reactor volume, heating only being applied to the last two thirds down to the outlet. Furthermore, the feed of the reaction mixture was increased to 60 ml/min, and the rotation speed

[0216] Thus, as may be taken from the results of the simulation displayed in FIG. 7, under the conditions chosen the reaction mixture displays an irregular velocity profile along the first third of the reactor volume, wherein the velocity regularly oscillates between values of around 0.2 m.Math.s.sup.1 and values of around 0.8 m.Math.s.sup.1, thus indicative of an at least intermittently if not substantially turbulent flow regime. Said velocity contour however diminishes to become constant at values of around 0.45 m.Math.s.sup.1, which is then observed throughout the remaining length of the reactor volume down to the outlet and is again indicative of a laminar flow regime within that portion of the reactor volume. Furthermore, as may be taken from the temperature contour displayed in FIG. 8, the first third of the reactor length is not heated and thus displays a temperature of 300 K, which is the temperature the reaction mixture has prior to entering the reactor. In the last two thirds of the reactor length in which the reaction mixture is heated, the second third displays a gradual increase to values of around 480 K, said temperature then being maintained in the last third of the reactor length down to the outlet. Thus, the reaction mixture in the last two thirds of the reactor volume displays a velocity and temperature contour resembling the results obtained in Example 1.

Reference Example 1: Viscosity Measurements Performed on a Reaction Mixture for Producing Chabazite

[0217] A reaction mixture for the synthesis of chabazite employing N,N,N-trimethylcyclohexylammonium hydroxide was prepared as described in WO 2013/182974 A1. The viscosity characteristics of said reaction mixture were then measured under reaction conditions, wherein the mixture was place in a rotational viscometer (Anton Paar, Physica MCR301) using a pressurized cell with cylindrical geometry (DG35, 12/PR). After placing a sample of the reaction mixture in the measurement cell, it was pressurized with nitrogen gas to a pressure of 8 bar. The viscosity was then measured, wherein the sample was heated from room temperature at a reaction rate of 2 C. per minute until 170 C. and then held constantly at that temperature. Three samples were measured at respective shear rates of 250 s.sup.1, 500 s.sup.1, and 750 s.sup.1, wherein the measurement for the shear rate of 250 s.sup.1 was interrupted after 119 minutes, the measurement for the shear rate of 750 s.sup.1 was interrupted after 142 minutes, and the shear rate of 500 s.sup.1 was interrupted after 300 minutes. The results of the measurement are displayed in FIG. 9. Thus, as may be taken from the results, the viscosity gradually decreases during the intial heating stage, wherein when reaching the maximum temperature it suddenly increases considerably, and then levels out until the end of the crystallization reaction, at which a further considerable increase of the viscosity is observed.

[0218] Accordingly, the viscosity measurement of the crystallization of the reaction mixture confirms the evolution of the rheology of the reaction mixture during the preparation of a zeolitic material as simulated in Example 3.

CITED PRIOR ART LITERATURE

[0219] US 2016/0115039 A1

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[0222] Vandermeersch, T. et al. in Microporous and Mesoporous Materials 2016, 226, 133-139

[0223] Liu, Z. et al. in Chemistry of Materials 2014, 26, 2327-2331

[0224] Slangen et al. Continuous Synthesis of Zeolites using a Tubular Reactor, 12.sup.th International Zeolite Conference, Materials Research Society 1999

[0225] Bonaccorsi, L. et al. in Microporous and Mesoporous Materials 2008, 112, 481-493

[0226] US 2001/0054549 A1